This section introduces aspects that may be helpful in facilitating a better understanding of the invention. Accordingly, the statements of this section are to be read in this light and are not to be understood as admission about what is in the prior art.
In 3GPP LTE (3GPP=3rd Generation Partnership Project, LTE=Long Term Evolution) for example it is suggested to use so-called fragmented bands by carrier aggregation for increasing the data rates in a wireless communication system. Thereby, the wireless communication system may be allowed to use a frequency band or a part of a frequency band of another wireless communication system, when one base station or several base stations of the other wireless communication system is/are not operated at full capacity. In such a case, an emission of a radio frequency signal by the wireless communication system in a frequency band still used by the other wireless communication must be prevented without fail.
Classical multicarrier signals such as OFDM multicarrier signals (OFDM=Orthogonal Frequency Division Multiplexing) are based on time domain signals having a rectangular shape. The rectangular shape in the time domain is associated with a shape of a so-called sinc-function in the frequency domain. Thereby, subcarriers of a multicarrier signal have rather high side-lobe levels. When using an OFDM multicarrier signal for the above mentioned application in fragmented spectrum, guard bands separating the fragmented sub-bands of the fragmented spectrum must be sufficiently large.
For upcoming machine-to-machine communication with low cost radio transmitters, synchronization requirements with respect to timing and frequency stability will likely be less stringent than for radio transmitters which are currently applied in cellular radio communication systems. Also so-called CoMP transmissions (CoMP=coordinated multipoint) exhibit timing offsets and frequency offset, when radio frequency signals propagate for example from two or more base stations via different propagation paths to a user terminal. The timing offsets may cause inter-carrier interference. By using conventional OFDM (OFDM=Orthogonal Frequency Division Multiplexing) subcarriers transmission quality degrades fast, when the timing offset exceeds the so-called cyclic prefix.
In so-called 5G future wireless systems, it is envisaged to relax synchronicity in terms of time and frequency between uplink users in order to reduce signaling overhead and device battery consumption. As a consequence, especially small packet messages and control information can be transmitted more efficiently than with strict synchronicity implying bulky random access procedures and closed-loop timing advance control.